Windows constructed from multiple glass panes utilized “muntins” or “muntin bars” to secure the edges of the individual glass panes within the window sash. In many windows, muntins formed distinctive grid patterns that are associated with architectural styles of buildings containing the windows.
Modern windows formed by insulating glass units utilize single glass lights separated by an insulating dead air space. Where a particular architectural “look” is desired, a grid of muntin bars is fixed in the dead air space between the glass lights to simulate a multi-pane window. Typical muntin bars for insulating glass units are formed from decoratively coated interfitted metal tubes. The grids are anchored to the insulating glass unit periphery.
Constructing muntin bar grids for insulating glass units has been a labor intensive process. As a consequence, manufacturing such units, and thus windows formed by the units, has been costly and inefficient. Some efforts to mechanize the manufacture of muntin grids have been made. Commonly owned U.S. Pat. No. 6,173,484 entitled “System for Fabricating Muntin Bars from Sheet Material” which issued Jan. 16, 2001 to McGlinchy et al. is an example of a system for automated fabrication of muntin bars. The subject matter of this patent is incorporated herein by reference. Commonly owned pending U.S. patent application Ser. No. 09/525,349 entitled “System for Fabricating Contour Muntin Bars from Sheet Material” is a second patent application to McGlinchy et al concerning automated fabrication of so-called contour muntin bars and the subject matter of this application is incorporated herein by reference.
The muntin bar stock is produced by roll forming decoratively coated sheet material such as aluminum or steel, in a known manner. Various sizes of the sheet material are used to form different size muntin bar stock. The roll forming machine has a series of rolls configured to form sheet material into elongated tubular muntin bar stock. A window manufacturer purchases the muntin bar stock size(s) needed to produce insulating glass units. Apparatus disclosed in the aforementioned patent application also cuts the stock into lengths that are notched in appropriate locations for assembly into grids for incorporation into the insulating glass units.
The residential window and door industry has witnessed an increased demand for internal decorative muntin bars contained in insulated glass (IG) units of their windows. This market demand for muntin bars has increased due to popular “colonial look” trends in the market which has increased the demand for simulated wood grain finishes for muntin bars. Also contributing to the demand are new construction and residential building codes requiring a common facade in local neighborhoods. With people also desiring differentiation and designer choices in their windows, a demand for so-called “two tone” muntin bars is on the rise. The two tone muntin bar present one appearance from the outside and a second appearance from inside the window.
Two-tone muntin bars are offered today in many color combinations for both rectangular and contour style muntin bars. A two-tone muntin bar demands a premium price in the market place. One reason for the increased price of two tone muntin bars is the fact that automated manufacturing of two tone muntin bars using controlled notching, roll forming and severing has not occurred.
The most common method practiced at the present time for manufacturing two tone muntin grids starts with a long roll formed bar that is often shipped to a secondary supplier that paints or laminates the bar with a solid color tone or pattern on one side and a second color or pattern on the opposite side. Use of multiple steps performed by multiple suppliers results in significant additional cost to the product. More elaborate bars have simulated wood grains that are used to match up with the wood trim in or surrounding the window sash. All of the current methods require cutting specified length segments from a two tone bar. This bar is then mitred and/or punched to complete fabrication of the muntin bar. The current methods require post painting and/or lamination which are time consuming, costly and provide limited throughput. This requirement also leads to a build up of inventory to give the suppliers adequate lead time for performing these post roll forming procedures.